Leeches were used for thousands of years as a medical tool, primarily to draw blood from patients in the belief that removing excess blood could cure disease. The earliest known depictions of medicinal leeching appear in ancient Egyptian paintings dating to around 1500 BC. From there, the practice spread across civilizations and peaked in 19th-century Europe before fading with modern medicine. Today, leeches have made a quiet comeback in one very specific surgical setting.
Ancient Origins Across Civilizations
Egyptian, Indian, Greek, and Arab physicians all used leeches to treat a remarkably wide range of conditions: skin diseases, dental problems, inflammation, nervous system disorders, and reproductive issues. The common thread was bloodletting, the idea that draining blood from a sick person could restore health. Leeches offered a controlled, relatively painless way to do this compared to cutting a vein with a blade.
The Greek physician Erasistratus went so far as to conclude that all disease resulted from an excess of blood. This idea became deeply embedded in Western medicine through a framework called humoral theory, which held that the body contained four essential fluids: blood, phlegm, yellow bile, and black bile. Health meant keeping these four in balance. Illness meant one was out of proportion, and blood was the easiest to remove.
How Humoral Theory Drove Leech Use
Under humoral theory, a person with too much blood was considered “hot and wet,” so drawing blood would cool and dry them, restoring equilibrium. Physicians placed leeches on different parts of the body depending on the location of the disease. A headache meant a leech on the face. Joint pain meant leeches near the affected joint. This location-based logic gave practitioners a sense of precision, even though the underlying theory was wrong.
Bloodletting through leeches became the standard treatment for an enormous list of conditions: plague, cancer, smallpox, rheumatism, acne, and headaches among them. For centuries, this wasn’t considered experimental or alternative. It was mainstream medicine, practiced by the most respected physicians in Europe and the Middle East.
The 1830s Leech Craze
Leech therapy hit its absolute peak in the early 19th century, especially in France. In 1832 alone, France imported 57.5 million leeches from various countries. Paris consumed two to three million leeches per year just within city limits. The demand was so intense that wild leech populations across Europe were driven to near-extinction, turning leeches into a global commodity traded across borders.
This “bleeding craze” eventually collapsed as medicine moved toward germ theory and more evidence-based treatments in the late 1800s. Physicians began to realize that draining blood from already-sick patients often made them weaker, not stronger. Leeches fell out of favor almost entirely for the better part of a century.
What Makes Leech Saliva Medically Useful
The irony of the leech story is that while the humoral reasoning was wrong, leech saliva turns out to contain genuinely powerful biological compounds. When a leech bites, it injects saliva packed with substances that thin the blood, prevent clotting, reduce inflammation, and widen blood vessels.
The most notable compound is a potent clot-preventing substance called hirudin, the strongest natural inhibitor of thrombin (the protein that makes blood clot) ever identified. Leech saliva also contains chemicals that stop platelets from clumping together and others that keep blood flowing freely through tiny vessels. This cocktail is what causes a leech bite to keep oozing blood for hours after the leech detaches, and it’s exactly what makes leeches valuable in modern surgery.
Leeches in Modern Reconstructive Surgery
In June 2004, the FDA cleared medicinal leeches as a prescription medical device for use in plastic and reconstructive surgery. This made them the first live animal formally regulated as a medical device in the United States. Two species are approved: one from northern Europe and one from southern Europe.
The primary modern use is treating venous congestion, a dangerous complication that occurs after surgeries involving reattached fingers, toes, ear reconstructions, skin flaps, and other microsurgery procedures. When tiny veins are damaged or not yet reconnected, blood flows into the reattached tissue through arteries but can’t drain back out. The tissue swells, turns purple, and without intervention, the trapped blood clots and the tissue dies.
Leeches solve this problem in two ways. First, they physically extract blood from the congested area. Second, their saliva prevents clotting and improves blood flow through the surrounding vessels, keeping the tissue alive long enough for the body to regrow its own venous drainage. A single leech typically feeds for about 45 minutes before detaching on its own, fully engorged. The bite site continues to ooze afterward, which provides additional relief from the congestion. Surgeons may apply leeches repeatedly over several days until circulation stabilizes.
Other Modern Applications
Beyond surgery, researchers have explored leech therapy for joint pain. A pilot study on knee osteoarthritis found that applying four leeches around the joint led to rapid pain relief, with sustained improvement lasting at least four weeks. The anti-inflammatory and blood-thinning properties of leech saliva likely drive this effect, though larger studies are still needed to confirm how well it works compared to standard treatments.
Risks of Leech Therapy
Medicinal leeches carry bacteria in their digestive tracts, particularly species of Aeromonas, which are the most common source of infection after leech therapy. Transmission rates in clinical settings range from about 2% to 36%, and infections can range from minor wound complications to serious bloodstream infections, especially in patients with weakened immune systems. For this reason, patients receiving leech therapy in hospitals are given preventive antibiotics before and during treatment. External cleaning of the leeches alone isn’t enough to eliminate the bacteria, since they live inside the leech’s gut.